Some Remarks on Quantum Coherence

There are many striking phenomena which are attributed to ``quantum coherence''. It is natural to wonder if there are new quantum coherence effects waiting to be discovered which could lead to interesting results and perhaps even practical applications. A useful starting point for such discussions is a definition of ``quantum coherence''. In this article I give a definition of quantum coherence and use a number of illustrations to explore the implications of this definition. I point to topics of current interest in the fields of cosmology and quantum computation where questions of quantum coherence arise, and I emphasize the impact that interactions with the environment can have on quantum coherence.Comment: 25 pages plain LaTeX, no figures. More references have been added and typos have been corrected. Journal of Modern Optics, in press. Imperial/TP/93-94/1

THE RING IMAGING CHERENKOV DETECTORS OF DELPHI

none98A Ring Imaging Cherenkov (RICH) detector system has been built and is now in full operation within the DELPHI experiment. Large data samples of Z(O) decays are being collected with good resolution on the observed Cherenkov angles. Several studies of Z(O) decays using the RICH have already been performed on limited samples. Disturbance of the detector operation caused by shrinkage of polymeric construction materials and by migration of radiator substance is reported. These effects have been counteracted and do not endanger the quality of the data.W. ADAM;E. ALBERECHT;D. ALLEN;M. ANDRIEUX;G. VANAPELDOORN;Y. ARNOUD;C. AUBRET;A. AUGUSTINUS;P. BAILLON;M. BATTAGLIA;M. BERGGREN;D. BLOCH;O. BOTNER;C. BOURDARIOS;J. BRUNET;A. BUDZIAK;A. BUYS;P. CARECCHIO;P. CARRIE;P. CAVALLI;G. CERUTTI;M. CHEVRY;E. CHRISTOPHEL;E. DAHLJENSEN;G. DAMGAARD;N. DIMITRIOU;B. DALMAGNE;M. DAVENPORT;J. DOLBEAU;M. DRACOS;M. DRIS;T. EKELOF;J. ENGEL;D. FASSOULIOTIS;T. FILIPPAS;E. FOKITIS;F. FONTANELLI;A. FONTENILLE;D. FRAISSARD;H. FURSTENAU;J. GARCIA;E. GAZIS;D. GILLESPIE;V. GRACCO;L. GUGLIELMI;F. HAHN;S. HAIDER;A. HALLGREN;W. HAO;P. HONORE;K. HUET;S. ILIE;P. IOANNOU;P. JUILLOT;E. KARVELAS;S. KATSANEVAS;E. KATSOUFIS;N. KJAER;P. KLUIT;B. KOENE;C. KOURKOUMELIS;G. LECOEUR;G. LENZEN;L. LINDQVIST;A. AGUERA;D. LOUKAS;S. MALTEZOS;A. MARKOU;J. MEDBO;J. MICHALOWSKI;F. MONTANO;G. MOURGUE;B. NIELSEN;R. NICOLAIDOU;T. PAPADOPOULOU;A. PETROLINI;D. POUTOT;G. POLOK;H. RAHMANI;M. REALE;L. RESVANIS;G. SAJOT;M. SANNINO;E. SCHYNS;S. SQUARCIA;P. STASSI;R. STRUB;J. THADOME;G. THEODOSIOU;M. TOBAR;D. TOET;L. TRASPEDINI;G. TRIPODI;G. TRISTRAM;A. TSIROU;O. ULLALAND;A. DELAVEGA;M. ZAVRTANIKW., Adam; E., Alberecht; D., Allen; M., Andrieux; G., Vanapeldoorn; Y., Arnoud; C., Aubret; A., Augustinus; P., Baillon; M., Battaglia; M., Berggren; D., Bloch; O., Botner; C., Bourdarios; J., Brunet; A., Budziak; A., Buys; P., Carecchio; P., Carrie; P., Cavalli; G., Cerutti; M., Chevry; E., Christophel; E., Dahljensen; G., Damgaard; N., Dimitriou; B., Dalmagne; M., Davenport; J., Dolbeau; M., Dracos; M., Dris; T., Ekelof; J., Engel; D., Fassouliotis; T., Filippas; E., Fokitis; Fontanelli, Flavio; A., Fontenille; D., Fraissard; H., Furstenau; J., Garcia; E., Gazis; D., Gillespie; Gracco, Valerio; L., Guglielmi; F., Hahn; S., Haider; A., Hallgren; W., Hao; P., Honore; K., Huet; S., Ilie; P., Ioannou; P., Juillot; E., Karvelas; S., Katsanevas; E., Katsoufis; N., Kjaer; P., Kluit; B., Koene; C., Kourkoumelis; G., Lecoeur; G., Lenzen; L., Lindqvist; A., Aguera; D., Loukas; S., Maltezos; A., Markou; J., Medbo; J., Michalowski; F., Montano; G., Mourgue; B., Nielsen; R., Nicolaidou; T., Papadopoulou; Petrolini, Alessandro; D., Poutot; G., Polok; H., Rahmani; M., Reale; L., Resvanis; G., Sajot; Sannino, Mario; E., Schyns; Squarcia, Sandro; P., Stassi; R., Strub; J., Thadome; G., Theodosiou; M., Tobar; D., Toet; L., Traspedini; G., Tripodi; G., Tristram; A., Tsirou; O., Ullaland; A., Delavega; M., Zavrtani